The advent of scanning force microscopy (SFM), also known as atomic force microscopy (AFM), has brought an instrument capable of microscopic surface studies with atomic resolution, suited for ambient and liquid environments and a wide variety of samples. SFM is a method for observing nanoscale topography and other properties of a surface. In general, SFM scans a force sensor over a surface.
SFM can be carried out in contact and non-contact modes. In a contact mode of operation, a topographical image is produced by measuring the deflection of a small cantilever beam extending from a mount end to a tip end bearing a sharp probe. Higher areas of the surface deflect the cantilever more. This deflection is typically detected by reflecting a laser beam off of the back of the cantilever onto a photodiode that is connected to provide its output signal to a computer, which converts the signal into a number. SFM can also be carried in an intermittent contact mode, in which the tip is brought closer to the sample than in a full non-contact mode so that at the bottom of its travel the tip just barely hits the sample.
SFM can be operated in either a constant height mode or a constant force mode. In a constant height mode, the height of the scanner is constant and the cantilever deflection can be used directly to generate the topographical data. In a constant force mode, the height of the probe above the surface is adjusted until the cantilever deflection value reaches a setpoint. The image is generated from the scanner height data. As the cantilever probe scans the surface, an image is produced based on the height of the scanner, pixel by pixel, with the darkness of each pixel representing the height data at that pixel.
Non-contact modes differ from the contact mode in that the cantilever is typically driven to oscillate, typically at its resonant frequency, and the amplitude, phase or frequency or a combination of these parameters is measured, e.g., by a laser beam and photodiode. As the probe approaches the surface, the amplitude of cantilever oscillation or the resonant frequency of the cantilever beam changes due to interactions with the surface. A feedback loop adjusts the height of the scanner to keep the cantilever vibrational amplitude or the cantilever vibrational frequency at a constant value, which also maintains the average tip to sample distance constant, and the height of the scanner at each data point in the scan over the surface is recorded. The low force applied to the sample in the non-contact mode makes it particularly useful for imaging soft samples, for example, DNA-protein complexes.
The cantilever beams and attached probe tips used in SFM are subject to wear and tear during use, especially in contact or intermittent contact modes where the probe tip repeatedly contacts the sample. For this reason, the cantilever beams and probe tips must be replaced from time to time. Although commercial replacement cantilever tips are widely available, most replacement tips are produced in clean rooms using a microlithography process similar to that used to make semiconductor chips. These types of processes are relatively expensive, so that commercially available replacement tips typically cost at least $100 for a single replacement cantilever tip. Consequently, the cost of replacement cantilever tips can be a barrier, especially in educational or research settings.
Most commercially available replacement cantilever tips are formed of silicon or silicon nitride. These materials are relatively brittle and inflexible, making them relatively susceptible to damage during use compared to other materials, such as plastics, which are more pliable. These materials are also opaque, so they obscure the sample area being imaged more than other materials, such as plastics, which can be transparent or translucent. The electrical properties of these materials can also cause problems in some applications, compared to other materials, such as plastics, which are electromagnetically insulating. Although there have been a few reports of the use of plastic probes for scanning force microscopy, replacement plastic cantilevers are not widely available commercially.
Thus, there is a need for a device and method which can produce plastic cantilevers for scanning force microscopes quickly, economically, and reliably. What is further needed is a method that can produce large numbers of such plastic cantilevers in a batch process. What is further needed is a method that can produce plastic cantilevers that are durable and electromagnetically insulating. What is further needed is a method that can produce plastic cantilevers that are adapted for magnetic force microscopy.